[Zope] Zope loose changed data after restarting

Hi! This is the second time we have lost changed data after restarting our web server. The data has been changed normaly from our website and also from Zope Manager Interface (add/modify/delete scripts, methods, etc). After we restart the server (it hangs) the history show us changed made >2 hours before. Even in the Zope logs there is no register about the changes. The changes just disappear. Why? We use: Zope 2.6.0, python 2.1.3 and CMF 1.4 Miguel